Ventilating device for motor vehicle fuel tank

ABSTRACT

The invention concerns a ventilating device for a motor vehicle fuel tank wherein a valve ( 12 ) is equipped with a ball ( 20 ) arranged in a chamber ( 14 ) wherein emerges an intake orifice ( 16 ) which opens into the center of a lower wall ( 19 ) concave upper surface ( 22 ) of the chamber ( 19 ), the ball ( 20 ) being supported on the concave upper surface ( 22 ). The invention is characterised in that the slope, relative to the horizontal, of the concave upper surface ( 22 ) decreases in the direction radially away from the axis (A 1 ).

The invention relates to a venting system for an automobile vehicle fueltank.

The invention relates more particularly to a venting system for anautomobile vehicle fuel tank of the type in which a valve is providedwith a ball which is placed in a chamber into which open an inletorifice which has an axis and is connected to the tank and an outletorifice, one orifice opens onto the center of a concave top face of abottom wall of the chamber, the ball bears on the concave top face sothat, when the vehicle is stopped and is substantially horizontal, theweight of the ball places it at the center of the concave surface whereit closes the orifice whereas the ball is moved away from the orifice byvibrations generated by starting or movement of the vehicle and enablesventing of the tank.

In the above type of system the top face of the inside wall of thechamber is usually circular and frustoconical with a vertical axis sothat as soon as the vehicle is stopped the ball drops to the bottom ofthe cone to shut off the orifice at the center of the cone.

The angle at the apex of the cone is dictated by a number of parametersrelated in particular to the maximum inclination of the vehicle whenstopped and the size of the ball, its size conditioning its weight andtherefore conditioning closing of the valve when filling the tank causesa positive gas pressure in the tank which must not escape via theventing system.

This latter parameter, which conditions the sealing effect of the valvewhen the vehicle is stopped, therefore makes it necessary to arrive at acompromise between the diameter of the ball and the angle at the apex ofthe cone formed by the top bearing face of the valve. To avoid using aball of excessively large diameter it is therefore necessary to use abearing surface having a relatively small angle at the apex.

Using a small angle at the apex means that the ball remainssubstantially at the center of the frustoconical surface, even when thevehicle is moving, and thereby interferes with the flow of the gasesthrough the valve.

An object of the invention is therefore to propose a new venting systemof the above kind which reduces the size and therefore the cost of theball and also satisfies simultaneously two contradictory requirements,namely a good seal of the valve when the vehicle is stopped and freeflow of the gases through the valve when the vehicle is moving.

To this end, the invention proposes a venting system for an automobilevehicle fuel tank of the type in which a valve is provided with a ballwhich is placed in a chamber into which open an inlet orifice which hasan axis and is connected to the tank and an outlet orifice, one orificeopens onto the center of a concave top face of a bottom wall of thechamber, the ball bears on the concave top face so that, when thevehicle is stopped and is substantially horizontal, the weight of theball places it at the center of the concave surface where it closes theorifice whereas the ball is moved away from the orifice by vibrationsgenerated by starting or movement of the vehicle and enables venting ofthe tank, characterized in that the inclination to the horizontal of theconcave top surface decreases in the radial direction away from theaxis.

According to other features of the invention:

the inclination varies continuously;

the inclination varies discontinuously;

the concave top face includes a frustoconical central first annular partaround the orifice to be closed, with its larger end at the top, whichhas a vertical axis and forms a bearing surface for the ball when thelatter is in the closing position, and in that the concave top surfaceincludes a frustoconical peripheral second annular part, around thefirst part, also with its larger end at the top, which has a verticalaxis and whose angle at the apex is greater than that of the bearingsurface so that it has a shallow slope;

the peripheral part has an angle at the apex of the order of 160degrees;

the bearing surface has an angle at the apex of the order of 145degrees; and

the ball has a diameter of approximately 12.7 mm.

Other features and advantages of the invention will become apparent onreading the following detailed description, which refers to theaccompanying drawings, in which:

FIG. 1 is a diagrammatic sectional view of a valve of a venting systemconforming to the teachings of the invention, shown when the vehicle isstopped;

FIG. 2 is a view similar to that of FIG. 1, showing the valve when thevehicle is moving;

FIG. 3 is an enlarged view of a detail from FIG. 1 showing moreparticularly the difference in cone angle of the bearing surface partcompared to the peripheral part of the valve according to the invention.

In a manner that is known in the art, for example as described in thedocument FR-A-2 740 402, automobile vehicle fuel tanks are generallyprovided with a venting system which includes a vent pipe which has abottom portion which opens into the tank at the top of the tank and atop portion which is connected to a vapor recovery and filter system,for example. A valve is included between the top and bottom portions ofthe vent pipe.

The venting system compensates the fall in the fuel level in the tank byenabling air to enter the tank so that the pressure therein issubstantially constant.

In contrast, the system must also enable evacuation of gases compressedbecause of an increase in temperature, for example, to avoid deformationof the tank which could cause it to rupture.

However, it is desirable for the vapor in the tank to be unable toescape directly to the atmosphere when the vehicle is stopped, whetherby evaporation or when filling the tank with fuel.

The venting system 10, a portion of which is shown in the figures,therefore includes a valve 12 for closing the venting circuit when thevehicle is stopped.

The valve 12 includes a chamber 14 which has at least one inlet orifice16 and one outlet orifice 18. The inlet orifice 16 passes through abottom horizontal wall 19 which delimits the chamber 14, is delimited byan inside cylindrical surface 17, has an axis A1 and is connected to thefuel tank, for example. The outlet orifice 18 opens into a lateral ortop wall of the chamber 14, for example.

A ball 20 is provided inside the chamber 14 and its weight presses itonto the top face 22 of the bottom wall 19 of the chamber 14. Accordingto the teachings of the invention, the top face 22, into which theorifice 16 opens, has a circular annular central first part 24 which isfrustoconical, with the larger end at the top, and has a vertical axisA1. The annular central part 24 is adapted to form a bearing surface forthe ball 20 when the vehicle is stopped, as shown in FIGS. 1 and 3.

Around the bearing surface 24 the top face 22 has a peripheral part 26,on which the ball 20 is moved by vibration generated when the vehicle isstarted or moving, which is also frustoconical, with the wider end atthe top, and has a vertical axis A1.

According to the teachings of the invention, and as can be seen in FIG.3 in particular, the frustoconical bearing surface 24 has a half-angle αat the apex which is less than the half-angle β at the apex of theperipheral part 26.

The bearing surface 24 therefore has an inclination to the horizontalwhich is greater than that of the peripheral part 26.

The slope of the peripheral part 26 can be relatively shallow.Consequently, the angle β can be relatively large. The only constrainton the angle β is that the ball must necessarily return to the center ofthe top face 22 regardless of the position of the vehicle relative tothe horizontal when stopped. Thus a half-angle at the apex ofapproximately 80° can be chosen for the frustoconical peripheral bearingsurface 26, i.e. an angle at the apex of approximately 160 degrees.

In contrast, when the ball 20 is in the closing position, bearing on thebearing surface 24, it is not sufficient for it to be held in thatposition. It is also necessary for the ball 20 to be able to resist apositive pressure in the tank, for example due to the fact that the tankis being filled with fuel, even if the vehicle is not horizontal.

If the vehicle is not horizontal, the resultant of the force of gravityon the ball is no longer coaxial with the axis A1 of the orifice 16 andthe bearing surface 24. Consequently, the force needed to raise the ball20 generated by the pressure of the gases on the bottom part of the ballclosing the orifice 16 represents only a small percentage of the weightof the ball.

To prevent the ball from being lifted, there is therefore a choicebetween reducing the half-angle at the apex of the frustoconical bearingsurface 24 or increasing the diameter of the ball. However, the lattersolution has the drawback of increasing its cost and overall size.

A good compromise might be to choose a ball with a diameter of 12.7 mm,for example, and a frustoconical bearing surface 24 whose half-angle atthe apex is approximately 72.5°, representing an angle at the apex of145 degrees.

The diameter of the inlet orifice 16 must be less than that of the ball20, of course, but it must also be less than the diameter of the contactcircle where the ball 20 bears on the bearing surface 24. The diameterof the orifice 16 must therefore be less than the diameter of the ball20 multiplied by the sine of the half-angle at the apex of the bearingsurface 24.

This cone angle assures effective retention of the ball 20 in theclosing position, but if vibration causes the ball 20 to move toward theperipheral part 26 it is no longer returned too forcefully toward thecenter of the top face 22.

Accordingly, by virtue of the new two-part design of the top face 22 onwhich the ball 20 rests, it is possible to obtain both a good seal atthe valve when the vehicle is stopped, including if the vehicle issteeply tilted, and, in contrast, free flow of the gases through thevalve 12 if vibration of the moving vehicle moves the ball 20 toward theperipheral part 26.

In the embodiment of the invention that has just been described there isa discontinuity in the slope between the bearing surface 24 and theperipheral part 26. These two parts of the top face 22 could of coursebe joined by a surface element such that the slope is variedcontinuously along a radius extending out from the axis A1.

Similarly, the two parts 24, 26 need not have strictly frustoconicalsurfaces. However, the slope of the top face must decrease overall inthe radial direction away from the axis A1.

What is claimed is:
 1. A venting system for an automobile vehicle fueltank of the type in which a valve (12) is provided with a ball (20)which is placed in a chamber (14) into which open an inlet orifice (16)which has an axis (A1) and is connected to the tank and an outletorifice (18), one orifice (16) opens onto the center of a concave topface (22) of a bottom wall (19) of the chamber (14), the ball (20) bearson the concave top face (22) so that, when the vehicle is stopped and issubstantially horizontal, the weight of the ball (20) places it at thecenter of the concave surface (22) where it closes the orifice (16)whereas the ball (20) is moved away from the orifice (16) by vibrationsgenerated by starting or movement of the vehicle and enables venting ofthe tank, characterized in that the inclination to the horizontal of theconcave top surface (22) decreases in the radial direction away from theaxis (A1).
 2. A venting system according to claim 1, characterized inthat the inclination varies continuously.
 3. A venting system accordingto claim 1, characterized in that the inclination variesdiscontinuously.
 4. A venting system according to claim 3, characterizedin that the concave top face (22) includes a frustoconical central firstannular part (24) around the orifice to be closed, with its larger endat the top, which has a vertical axis (A1) and forms a bearing surfacefor the ball (20) when the latter is in the closing position, and inthat the concave top surface (22) includes a frustoconical peripheralsecond annular part (26), around the first part (24), also with itslarger end at the top, which has a vertical axis (A1) and whose angle(β) at the apex is greater than that (α) of the bearing surface (24) sothat it has a shallow slope.
 5. A venting system according to claim 4,characterized in that the peripheral part (26) has an angle (β) at theapex of the order of 160 degrees.
 6. A venting system according toeither claim 4 characterized in that the bearing surface (24) has anangle (α) at the apex of the order of 145 degrees.
 7. A venting systemaccording to claim 1, characterized in that the ball (20) has a diameterof approximately 12.7 mm.